The two streams meet at a confluence. It takes many tributary streams to form a river. A river grows larger as it collects water from more tributaries. Streams usually form rivers in the higher elevations of mountains and hills. The areas of depression between hills or mountains are known as valleys.
The world's fastest production single piston engine aircraft produced in Great Britain, deployed from 1945 to 1953. Heavily Modified Sea Fury aircraft can be seen today as air racers. Heinkel He-162 562 mph. Arguably the fastest WW II jet fighter.
The NASA X-43 was an experimental unmanned hypersonic aircraft developed by NASA as part of its Hyper-X program. It is the fastest aircraft on record with a top speed of an incredible Mach 9.6 (7,310 MPH). The X-43 was placed on top of a solid fuel booster rocket, which was itself a modified version of the Pegasus rocket, and then drop launched from a carrier plane.